U.S. Navy guided-missile destroyer collided with a Japanese-owned bulk oil tanker  Sunday near the Strait of Hormuz, at the mouth of the Persian Gulf.

The crash occurred about 1 a.m. local time. The cause of the incident is under investigation, but the Navy said it was “not combat related.” No one was injured, and no spills or leakages were reported from either vessel. The USS Porter had a large hole on its starboard side but was able to operate under its own power, according to a news release from the U.S. Navy.

Maritime attorneys know that one-fifth of the world’s oil is routed through the Strait of Hormuz. Tensions in the region have been high, with threats from Iran to block tanker traffic in response to tighter sanctions.